faulty report and no reports no service

Bought suzuki alto 2011 model now on 80000km got her on 1st of April 2015 at Durban rally motors pinetown. At the time I received het the car idle high and up down up down up down. I went to suzuki witbank on 28April after I asked around why the car does that and is high on fuel. They said it is the tpc sensor that regulates the idle and temperature. Suzuki tested her on 28april said it is the sensor they will order I received the new one yesterday only and it still does the same thing I went back to them the computer does not pick up anything after the whole day with them today they tell me it is the cpu, but why? They can't give me any diagnose report for saying that the computer of car is damaged. I mean my car is just bought like that and no one can assist me on the real problem after paying for that sensor that they said it's the problem and now it's the cars brain, are they ever going to help me and give me any proof? And going to get my money back on that part? I never though that suzuki will give me trouble at all. I want my car fixed to the correct fault and do not want to be taken for a fool and I will proof that they are wrong why can't they provide me the report or any?